Fix Redis singleton: prevent retry storm on init failure

src/data/redis_cache.py

@@ -29,16 +29,19 @@ log = logging.getLogger(__name__)
 # ---------------------------------------------------------------------------
 
 _instance: Optional["RedisCache"] = None
+_init_failed: bool = False
 _lock = threading.Lock()
 
 
 def get_redis() -> Optional["RedisCache"]:
     """Return the global RedisCache instance, or *None* if not configured."""
-    global _instance
+    global _instance, _init_failed
 
     # Fast path (no lock)
     if _instance is not None:
         return _instance
+    if _init_failed:
+        return None
 
     url = os.environ.get("UPSTASH_REDIS_URL")
     token = os.environ.get("UPSTASH_REDIS_TOKEN")
@@ -50,12 +53,15 @@ def get_redis() -> Optional["RedisCache"]:
         # Double-check after acquiring lock
         if _instance is not None:
             return _instance
+        if _init_failed:
+            return None
         try:
             _instance = RedisCache(url=url, token=token)
             log.info("Redis connected: %s", url.split("@")[-1] if "@" in url else url[:40])
             return _instance
         except Exception as exc:
-            log.error("Redis init failed: %s", exc)
+            _init_failed = True
+            log.error("Redis init failed (will not retry): %s", exc)
             return None